The eye is a vital organ that provides sight, which is both anatomically and immunologically privileged. This means that while the organ is protected physiologically, it is also resistant to penetration by foreign substances such as drugs. Ocular drug delivery development has led to a multitude of approaches and systems that vary in mode of administration, implantation site, composition and vehicles. Such systems aim to circumvent the problems of drug bioavailability, sustainability and feasibility of the system as well as reduce the effect of the single major cause of poor therapeutic response from poor patient compliance.
There are many diseases of the eye that require constant administration of a bioactive agent, either life-long such as in the treatment of glaucoma or in severe ocular surface immune disorders, or for prolonged periods (months) such as after surgery.
Full thickness corneal transplantation (Penetrating keratoplasty (PK)) has been the standard surgical treatment for corneal blindness for many years. Improvements over the last quarter of a century in surgical instrumentation and transplantation techniques, and advancements in the management of immune rejection, post-operative inflammation, cataracts and glaucoma have lead to steady improvements in corneal graft survival.
Despite these advances, the long-term outcome of PK still remains far from ideal; data from corneal graft registries of industrialized countries suggest that the overall 10-year survival rate may be as low as 50%, whilst the Singapore Cornea Transplant Study (SCTS) found that the overall 10-year survival of optical grafts to be no better for Asian patients (52.0%). Following corneal transplantation, patients require intensive steroid medication for at least one year. The development of sustained release steroid formulation will significantly improve drop compliance post keratoplasty. In high risk cases, steroid therapy is supplemented by the use of steroid sparing immune-modulating agents e.g. cyclosporine, mycophenolate. The development of sustained drug release formulations of these drugs will aid in compliance and contribute to long-term graft survival in these high risk cases. The development of a sustained release anti-angiogenic drugs will aid in reducing the preoperative effects of multiple quadrant corneal vascularization and hence improve corneal graft survival. The mainstay of treatment involves the use of intensive topical steroids. The development of a sustained release steroid releasing delivery device will significantly improve drop compliance in cases of graft rejection.
Several other ocular surface disease e.g. vernal keratoconjunctivits, allergic eye disease, require the chronic use of intensive immunosuppressants. The development of sustained release steroids as well as other immunosuppressant agents will allow for better control of these inflammatory ocular surface diseases.
Sustained delivery for antibiotics, anti-inflammatories, anti-scarring as well as anti-glaucoma medications would revolutionise ophthalmic medical therapy.